Internal combustion heater having means for relief of pulsations



FAIRBANKS INTERNAL COMBUSTION HEATER HAVING MEANS Aug. 6, 1957 J FOR RELIEF OF PULSATIONS original'F'iled Aug. 29, 1950 United States Patent "cc INTERNAL COMBUSTION HEATER HAVING NIEANS FOR RELEF F PULSATIONS Gordon J. Fairbanks, Indianapolis, Ind., assignor to Stewart-Warner Corporation, Chicago, Ill., a corporation of Virginia Original application August 29, 1950, Serial No. 182,021, now Patent No. 2,699,813, dated January 18, 1955. Divided and this application March 15, 1954, Serial No. 416,194

3 Claims. (Cl. 158-1) The present invention relates to improvements in the internal combustion heaters of the sealed combustion chamber type to improve their operating and fuel burning characteristics particularly when such heaters are equipped with long exhaust pipes. A typical sealed combustion heater is illustrated in United States Letters Patent No. 2,507,081 issued May 9, 1950.

This application is a division of the copending application of Gordon J. Fairbanks, Serial No. 182,021 filed August 29, 1950, Patent No. 2,699,818, dated January 18, 1955, which in turn is a continuation in part of the now abandoned application Serial No. 682,940 filed July 11, 1946. 1

Certain types of combustion heaters, particularly those in which the combustion chamber is sealed so that u the products of combustion are carried from the heater to the atmosphere through a long exhaust pipe without the possibility of contaminating the surrounding, air, have the unfortunate characteristic of rough running. Such rough running causes inefiicient combustion and under some conditions may cause the combustion to become so unstable as to be unreliable. It has been found that as a general rule the longer the exhaust pipe the greater the roughness in the heater combustion, so that it has been proposed in some instances to install heaters of the sealed combustion chamber type only under conditions where a comparatively short exhaust would lead to the outside atmosphere. The disadvantages of such a scheme are apparent and are overcome by the present invention.

The rough running in a sealed'combu-stion type heater is caused by pulsations in the burning gases which occur regularly and rapidly though at different rates or frequencies for heaters of different designs and sizes.

These pulsations are very likely caused by the rapid intermittent expansion of the burning gases. If the heater has substantially no resistance or back pressure at its exhaust outlet, this expansion takes place in the direction of low resistance, namely toward the exhaust. However, when the heater is titted with a long exhaust pipe of perhaps eight or ten feet, a long air or exhaust gas column must be moved by the burning gases. Since the gas column in the exhaust pipe or system offers a very great resistance or inertia to the sudden expansion of burning gases in the exhaust direction, at least a part of this expansion causes a rapid rise in pressure at the combustion air inlet. Since the air for combustion is being fed under pressure, it eventually overcomes the momentary burning gas expansion towards the inlet and the whole mass ultimately-moves toward the exhaust outlet. However, the momentary break in the constant and 'even flow of air for combustion slows down the burning 7 2,801,685 Patented Aug. 6, 1957 sion thereof to repeat the cycle. It appears that more or less rapid alternating high and low pressure conditions are present in the combustion chamber. These high and low pressures cause fluctuations in the ratio of fuel to combustion air and consequently in the rate of combustion. It will be appreciated that these fluctuations in ratio and rate have an adverse effect on combustion and under some extreme conditions will quench it.

It is, therefore, the principal object of the present invention to provide a novel combustion heater of the sealed combustion chamber type having means to prevent rough running or pulsations in combustion. I

Another object is to provide a novel combustion heater of the sealed combustion chamber type which may have an exhaust pipe of any convenient length and yet does not possess the disadvantages in pulsating combustion normally attendant upon long exhaust pipes.

Another object is to provide a novel combustion heater wherein the exhaust gases are at least partially vented near the exhaust end of the heater and in such manner as not to contaminate the surrounding air.

Another object is to provide a novel combustion heater wherein the vented fraction of the exhaust gases are recirculated with fresh air for combustion.

Still another object is to provide an exhaust system for an internal combustion heater having a long exhaust pipe wherein a minor portion of the products of combustion are vented immediately adjacent the heater exhaust outlet while the major portion are exhausted at a point remote from the heater.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing, wherein:

Fig. 1 is an elevational view partially broken into section of an internal combustion heater incorporating the present invention; and

Fig. 2 is an elevational view partially broken into section of the heater of Fig. 1, taken from the right or exhaust end of the heater. In this figure a portion of the exhaust system is turned from its normal position and is H includes an outer casing 12 enclosing a burner 14 and a heat exchanger 16. Air for combustion is supplied by a blower 18 driven by a motor 20 to deliver air through a duct 22, fitting 24, and conduit within the heater to the burner 14. Fuel in a liquid state is supplied through a control valve 26 and conduit 28 to a chamber or pocket 30 which also encloses an igniter 32 of suitable type. The valve 26 may be of any convenient type which is for the purpose of turning the heater off and on and under some conditions may also operate to modulate the heat output between high and low conditions.

From the heatexchanger, the products of combustion flow through an exhaust spud 34 and through an exhaust system 36. Airfor ventilation is supplied to the heater casing 12 from a blower 38 driven by a motor 40. The heater may be equipped with any suitable control system for turning the heater on and off in response to combustion detection and overheat conditions in the heater. Such controls have not been illustrated inasmuch as they form no part of the present invention.

The heat exchanger 16 includes three generally concentric shells 42, 44 and 46. The inner shell 42, which is closed at the right end by a panel 47, and at the left end by the burner structure 14, defines primarily the combustion chamber. Air to be heated is forced longitudinally of the heater between the shells 42 and 44 and between the shell 46 and, the casing 12 by the blower 38. The space enclosed by the shells 44 and 46 constitutes a path for the flow of the products of combustion which are received from the combustion chamber through a slotted opening 48 in the shells 42 and 44 and extending a substantial distance longitudinally of the heater. The shell 44 is offset inwardly at 50 at both sides and the end of the slot 48 to bear against the shell 42 to which it is electrically seam-welded to form a gastight joint. The slot 48 is diametrically opposite the exhaust spud 34 so that the exhaust gases will be forced in two paths in the annular space between the shells 44 and 46 to the exhaust opening. This annular space is closed at either end of the heater by metal rings 52 welded to the shells 44 and 46. Opposite the slot 48 and adjacent the exhaust spud 34 the shells 42 and 44 are formed with abutting spacing bosses 54, and the casing 12 is properly supported around the shell 46 by a plurality of spacers 56.

The exhaust system 36 includes an acoustical detuning T fitting 58 which is secured to the exhaust spud 34 by any conventional means such as screws 60. An exhaust pipe 62 of length which may be dictated according to the circumstances and conditions under which the heater is to be used is similarly connected to the T fitting 58. The exhaust T fitting 58 includes a stem forming a relatively short spud 64 intermediate its ends and extending generally at right angles to its longitudinal axis and having a substantially smaller diameter than the diameter of the fitting 58. It has, however, free communication with the main body of the fitting 58.

The combustion air blower has an inlet housing or casing 66 to which a flexible conduit 70 is secured by a suitable removable type clamp 72. The conduit 70 is in turn connected to a reduced extension 76 of a hatshaped member 78 by a fastening clamp 80. The outer flange 82 of the member 78 is secured as by spinning or welding to a cylindrical inlet sleeve or housing 84. The sleeve 84 is supported on the T-fitting 58 by a pair of angle brackets 86 each of which has one leg spotwelded to the outer surface of the fitting 58 and the i.

other leg 88 projecting outwardly therefrom. If desired, the housing 84 may be spot-welded to the legs 88 or the latter may be biased outwardly of each other so as resiliently to grip the inner wall of the cylindrical inlet.

It will be apparent from Fig. 2 that the outer end of the sleeve 84 is not pushed onto the brackets 86 so as to contact the fitting 58 but is spaced therefrom at 90 a short distance to provide an inlet clearance for the suction of combustion air into the inlet housing 84 and through the conduit 70 to the blower 18. It will be further observed that the housing encompasses the outer end of the spud 64 of the T fitting 58 so that the exhaust gases which are vented from the fitting 58 are introduced into the combustion air stream and recirculated by the blower 18. The fitting 58 is connected directly to the exhaust spud 34 from the heater to locate the vent spud 64 immediately adjacent the heater exhaust outlet so that expansion of gases within the heater due to the combustion may be immediately relieved to a point of low pressure.

The heater operates in substantially the following manner:

Combustion is initiated in the combustion chamber and burner 14 in the customary fashion by the igniter 32, and fuel is continuously fed to the burner through the fuel metering valve 26 and the pocket 30. Air for combustion is supplied by the blower 18 to the conduit 22, fitting 24, and heater conduit 25 to the burner 14 where it picks up fuel from a pool lying in the bottom of the burner well to form .a combustible mixture. Once the combustion is established in the combustion chamber the products of combustion circulate from the combustion chamber through the slot 48 and between the shells 44 and 46 to reach the exhaust spud 34. The major portion of the exhaust is expelled through the exhaust system 36 comprising the fitting 58 and exhaust pipe 62 and is exhausted to the atmosphere .at some convenient and perhaps remote place from the heater. The heater thus far described is that shown in the aforementioned Patent No. 2,507,081 which has proved to be quite satisfactory, but under some conditions when equipped with a relatively long exhaust pipe or an exhaust system creating excessive back pressure or inertia it is subject to the disadvantages discussed in the opening paragraphs of this specification.

It is to be noted, however, that with the provision of the venting spud 64 at a point closely adjacent the exhaust outlet 34 a portion of the exhaust gases is expelled from the exhaust system immediately adjacent the exhaust outlet. This relieves the back pressure which would otherwise be built up against the column of air and gases in the exhaust pipe 62. Fluctuations and expansions in the products of combustion arising in the burning gases within the combustion chamber are relieved and compensated through the exhaust spud 64 where no substantial back pressure of inertia is experienced.

In order to dispose of these gases without contaminating the air immediately surrounding the heater 10, these exhaust gases are dumped into the inlet to the combustion air blower 18 and are then recirculated to the burner 14. It has been found as a matter of practical experience that the introduction of a small fraction of exhaust gases into the combustion air inlet does not deleteriously affect combustion or heater operation. It is, therefore, seen that the disadvantages usually attendant upon the use of a relatively long exhaust pipe to convey the products of combustion to a convenient place in the atmosphere have been completely overcome by the provision of the secondary exhaust outlet 64 which introduces a portion of the products of combustion into the inlet of the combustion air blower.

While a preferred embodiment of the internal combustion heater constituting this invention has been shown and described, it will be apparent that modifications and variations thereof may be made without departing from the underlying principles of the invention. It is therefore desired by the following claims to include within the scope of the invention all such variations and modifications by which substantially the results of this invention may be obtained through the use of substantially the same or equivalent means.

What is claimed as new and desired to be secured by United States Letters Patent is:

1. In an internal combustion heater having a structure forming a sealed combustion chamber and heat exchanger, a blower for supplying combustion air thereto, an exhaust connection to receive and exhaust the products of combustion from the heat exchanger portion of the structure, and an exhaust pipe extending a substantial distance from the structure to a remote point, the improvement which comprises a relatively short, double ended, acoustical detuning, tubular fitting having one end connected to and communicating with the exhaust connection and the other end connected to and communicating with the exhaust pipe, said detuning fitting having a tubular spud projecting therefrom and forming an unobstructed vent passage communicating with said fitting between the ends thereof and immediately adjacent the exhaust connection for venting at least a portion of the products of combustion to relieve pressure pulsations in the burning gases in the combustion chamber and to prevent such pulsations from being communicated to the products of combustion in the exhaust pipe, conduit means having one end connected to the inlet end of the combustion air blower and having an open inlet end, and means supporting said inlet end of said conduit means from said fitting so that said inlet end encompasses said spud in spaced relation thereto for conducting products of combustion escaping through said vent passage in response to peak conditions of pressure pulsations in the burning gases to the combustion air blower for recirculation with combustion air.

2. In an internal combustion heater having structure forming a sealed combustion chamber and heat exchanger, a blower for supplying combustion air thereto, an exhaust connection to receive and exhaust the products of combustion from the heat exchanger portion of the structure, and an exhaust pipe extending a substantial distance from the structure to a remote point, the improvement which comprises a relatively short, double ended, T- shaped, acoustical detuning, tubular fitting having one end connected to and communicating with the exhaust connection and the other end connected to and communicating with the exhaust pipe, said detuning fitting having a projecting tubular spud forming an unobstructed vent passage communicating With the interior of said fitting between the ends thereof and immediately adjacent the exhaust connection for venting at least a portion of the products of combustion to a region of pressure lower than that in the combustion chamber to relieve pressure pulsations in the burning gases in the combustion chamber and to prevent such pulsations from being communicated to the products of combustion in the exhaust pipe, conduit means having one end connected to the inlet to the combustion air blower and having an open inlet end, and means mounting said inlet end on said fitting so that said inlet end encompasses said projecting spud in spaced rela- I tion thereto for conducting products of combustion escaping through said vent passage in response to peak conditions of the pressure pulsations in burning gases to the combustion air blower for recirculation with combustion air.

3. In an internal combustion heater having structure forming a sealed combustion chamber and heat exchanger, a blower for supplying combustion air thereto, an exhaust connection to receive and exhaust the products of com bustion from the heat exchanger portion of the structure, and an exhaust pipe extending a substantial distance from the structure to a remote point, the improvement which comprises a relatively short double ended, acoustical detuning, tubular fitting having one end connected to and communicating with the exhaust connection and the other end connected to and communicating with the ex haust pipe, said detuning fitting having a tubular spud projecting therefrom and forming an unobstructed vent passage communicating with the interior of said fitting between the ends thereof and immediately adjacent the exhaust connection for venting at least a portion of the products oi combustion to a region of pressure relatively lower than that in the combustion chamber to relieve pressure pulsations in the burning gases in the combustion chamber and to prevent such pulsations from being communicated to the products of combustion in the exhaust pipe, conduit means having one end connected to the inlet to the combustion air blower and having an open inlet end, said inlet end comprising a rigid open ended sleeve, and bracket means mounting said sleeve on said fitting so that said spud projects thereinto in spaced relation thereto so as to conduct products of combustion escaping through said vent passage in response to peak conditions of the pressure pulsations in the burning gases to the combustion air blower for recirculation with fresh combustion air.

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